This invention relates generally to the recovery of torpedoes and other objects from beneath the surface of water and more specifically to inflatable bags which produce positive buoyancy for bringing a torpedo to the water's surface.
Torpedo design and development efforts, particularly those directed to the more advanced torpedoes, require that prototype designs be "exercisable". Exercisability implies that the torpedo be capable of being configured in a nonexplosive version exhibiting the same physical characteristics and dynamic performance parameters as its warshot counterpart, so that it may be carried, launched, and run at sea against targets in the same manner as a warshot version would be. An exercise torpedo attempts to duplicate the salient characteristics of its warshot counterpart and is instrumented to record and make available data related to the dynamic performance of the torpedo and to its interaction with a target. More importantly, this data must be recoverable either by telemetry or by the physical recovery of the exercised torpedo itself. For economic reasons, recovery of the torpedo itself is generally considered preferable.
By design, all warshot torpedoes are negatively buoyant throughout their run. Unless the torpedo encounters a target, it will sink at the end of its run so that it does not become an explosive threat to friendly surface craft and cannot be retrieved by the enemy.
Current torpedo designs include larger warheads and are generally more densely packaged and include more powerful propulsion systems, causing greater negative buoyancy than that of previous torpedoes. The increased negative buoyancy and increased speed of the current torpedoes complicate recovery of the torpedo. Previously utilized recovery systems have proven inadequate for a variety of reasons.
In the past primarily three different methods have been employed for the recovery of torpedoes that have been exercised: (1) hoisting the torpedo from the floor of the body of water into which it was fired by means of hooks, lines, etc.; (2) providing positive buoyancy at the end of a run by weight dropping, and (3) providing positive buoyancy at the end of a run by increasing torpedo displacement. The third method, i.e., providing positive buoyancy at the end of a run by increasing torpedo displacement, has been successfully utilized with previous torpedo designs. All of these "displacement" systems include a balloon or bag attached to the torpedo when it is fired. A suitable gas generator within the torpedo is triggered by some event such as a change in torpedo speed, the increase of pressure beyond some threshold level, etc., and supplies gas for inflating the balloon or bag to create the desired positive buoyancy. Initiation of the gas pressurization system generally occurs upon torpedo propulsion power plant shut-down.
Various types of balloons, sleeves, collars, and other negative buoyancy configurations have been utilized in the past. However, as torpedoes have become faster and more dense, previously utilized designs have proven to be inadequate.
The most basic type of displacement system is a collapsible pontoon of the general type shown in U.S. Pat. No. 3,608,510. Pontoon systems cannot be used in the recovery of horizontally moving objects and are thusly not suitable for torpedoes.
A slightly different "balloon" system utilized for torpedoes is shown in U.S. Pat. No. 3,175,525. In such "balloon" systems a gas filled bag is ejected from the torpedo and tethered to the torpedo via a line. This type of system is effective only for relatively slow moving objects and is completely ineffective for the recovery of objects that roll. Torpedoes tend to roll while they descend and thus cannot use the "balloon"-type system.
Other displacement recovery systems utilize balloons attached to the nose end of a torpedo, such as shown by U.S. Pat. No. 1,998,805. A major drawback to this arrangement is that it is unsuitable for use with acoustic torpedoes, wherein the nose portion must remain free of obstruction to sound waves transmitted from and reflected sound waves received by the torpedo. In addition, this type of system is only useful with slow moving vehicles.
One of the more useful of the current displacement systems is the expandable collar of the type illustrated by U.S. Pat. Nos. 3,648,312 and 3,706,294. Such collars are fabricated from fabric-reinforced heavy material forming a closed bag. In order to provide a tapered shape for aiding deceleration of the torpedo being recovered, additional reinforcement fabric is provided at the forward end. A gas seal is provided only by the use of a closed bag. The use of such heavy walled, closed bags includes several disadvantages. They are complex, expensive to produce and extremely difficult to install. The use of a folded heavy bag requires a relatively deep recess in the exercise section of the torpedo not always tolerable with small torpedoes. Much of the surface area of the exercise section of the torpedo is covered by the inner wall of the bag (adjacent the outer surface of the torpedo) so that there is little room for anything else.